linux-kernel - Re: [PATCH] Tight check of pfn_valid on sparsemem

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1280436919.16922.11246.camel@nimitz>
Date:	Thu, 29 Jul 2010 13:55:19 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Milton Miller <miltonm@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>,
	Kukjin Kim <kgene.kim@...sung.com>
Subject: Re: [PATCH] Tight check of pfn_valid on sparsemem - v4

On Thu, 2010-07-29 at 19:33 +0100, Russell King - ARM Linux wrote:
> And no, setting the sparse section size to 512kB doesn't work - memory is
> offset by 256MB already, so you need a sparsemem section array of 1024
> entries just to cover that - with the full 256MB populated, that's 512
> unused entries followed by 512 used entries.  That too is going to waste
> memory like nobodies business.

Sparsemem could use some work in the case where memory doesn't start at
0x0.  But, it doesn't seem like it would be _too_ oppressive to add.
It's literally just adding an offset to all of the places where a
physical address is stuck into the system.  It'll make a few of the
calculations longer, of course, but it should be manageable.

Could you give some full examples of how the memory is laid out on these
systems?  I'm having a bit of a hard time visualizing it.

As Christoph mentioned, SPARSEMEM_EXTREME might be viable here, too.

If you free up parts of the mem_map[] array, how does the buddy
allocator still work?  I thought we required at 'struct page's to be
contiguous and present for at least 2^MAX_ORDER-1 pages in one go.  

-- Dave

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/